An Electrochemical cell for <i>in operando</i> <sup>13</sup>C NMR investigations of carbon dioxide/carbonate processes in aqueous solution

Abstract. In operando NMR spectroscopy is a method for the online investigation of electrochemical systems and reactions. It allows a real-time observation of the formation of products and intermediates, and it grants insight into the interactions of substrate and catalyst. An in operando NMR setup for the investigation of the electrolytic reduction of CO2 on silver electrodes has been developed. The electrolysis cell consists of a three-electrode setup using a working electrode of pristine silver, a chlorinated silver wire as reference electrode, and a graphite counter electrode. The setup can be adjusted for the use of different electrode materials and fits inside a 5 mm NMR tube, Additionally, a shielding setup was employed to minimize noise caused by interference of external radio frequency (RF) waves with the conductive components of the setup. The electrochemical performance of the in operando electrolysis setup was investigated in comparison to a standard CO2 electrolysis cell. The small cell geometry impedes the release of gaseous products, and thus it is primarily suited for current densities below 1 mA/cm2. The effect of conductive components on 13C NMR experiments was studied using a CO2 saturated solution of aqueous bicarbonate electrolyte. Despite the B0 field distortions caused by the electrodes, line widths of ca. 1 Hz could be achieved. This enables the investigation of interactions in the sub-Hertz range by NMR spectroscopy. It was found that the dynamics of the bicarbonate electrolyte change due to interaction with the electrochemical setup, by catalyzing the exchange reaction between CO2 and HCO3− and affecting the formation of an electrical double layer.